The Las Vegas anthrax scare highlights warnings by experts that deadly biological agents are fairly easy to obtain. 'The threat is here. The threat is real,' an FBI official says.

Even the classic terrorism scenario of dumping a vial of poison into a municipal water supply wouldn't work with anthrax--it would take tons of the poison to cause illness, according to Bill Patrick, who led the U.S. effort to develop biological weapons in the 1950s and '60s.

That said, however, Patrick acknowledged that biological weapons can be employed with devastating effectiveness on a smaller scale. Just a few grains of ricin can kill if pressed against the skin.

Patrick also points out that biological weapons are almost impossible to defend against because they are hard to detect until they begin their deadly work. Antibiotics can treat anthrax poisoning if prescribed immediately, but by the time symptoms develop it's often too late.

Patrick regularly travels the country to give lectures, carrying simulated toxins and dissemination devices in his briefcase. He said he has never been stopped at airport security. "The offense," he said, "has all the advantages over the defense."